Art of riveting



Patented Nov. 24, 1942 UNITED STATE ART OF BIVETING Louis s. Marsh, Kirkland, Wash assignor, by

mesne assignments, to Boeing Aircraft Company, Seattle, Wash., a corporation of Washmgton Application January 11, 1939, Serial No. 250,351

.Claims.

This invention has been designed as a method of riveting light sheets of relatively soft metal together, as sheets of aluminum or aluminum alloys, in the construction of aircraft, andusing aluminum alloy or other soft metal rivets, and it is particularly adapted to such uses in that by my method rivets can be left with flat heads flush with the exterior skin, surface, so that the finished exterior surface is flush and smooth throughout, and therefore aerodynamically efflclent, yet the rivets are intimately associated with the sheets and with the edges of the holes, and in that, by this invention, a high percentage of substantially perfect rivets may be formed by the normal workman without undue care or expenditure of time.

While it is to such ends that the present invention is particularly-directed, nevertheless by its use several other objects may be attained, or several individual objects, included or implied among the objects expressed above, will prove advantageous even though certain other such ends are not employed or objectives attained in the method as used. For instance, whether the head finally formed be flush or not, certain of the principles of the present invention provide an excellent and intimate engagement between the shank of the rivet and the edges of the holes in the sheets to be joined, thus by expansion of that part of the rivet shank which is within the holes assisting in forming a tight joint along the riveted seam, and about the shank and head of the rivet, and preventing that cooking of the rivet shank in the holes in the plate that precludes the formation of a high percentage of acceptable upset heads by a subsequent operation. Likewise, whether the head be left finally fiush or not, and whether the shank be thus expanded radially into intimate association-with the edges of the holes or not, the invention is of value in forming an intimate association be-- tween the bulged head, the bulge of which is reversed inrthe process of riveting, and the sheets, and in centering the backing tool so that force may be applied evenlyto the head, and the plates may be gripped and held together, for such a purpose as to reverse the bulge of the head. or to effect counterpunching of the sheets.

With these and other objects in mind, as will appear hereafter, my invention comprises the novel method of riveting and the novel tools for use in riveting, as shown in the accompanying drawing, described in this specification, and the fined by the claims which terminate this specification.

In the accompanying drawing I have shown successive steps in the riveting, in the preferred form, and the distinctive step in a' modification of the preferred process, the tools employed in riveting, and the final product as applied to a typical rivet and joint, it being understood, of

course, that the showing and the description hereafter are for purposes of illustration only.

Figure 1 is an axial section through a rivet I section, and in the other-half the grainof the .metal is indicated, to show the fact and effect of compression.

Figure 2 is a similar view showing the parts after the second step has been completed, and

Figure 3 is a similar view showing the completion of the third and final step of the preferred process.

Figure 4 is a view similar to Figure 1, but

showing, insection, the tools in position to begin the second step of the preferred process, and

, Figure 5 is a view similar to Figure 4, showing the tools employed and their relative position at the completion of the third step of the preferred process. Figure 6 is a view generally similar to Figure 1, the rivet being in elevation, however, showing the beginning of the third and final step of I the operation according to a modified plan.

Figure '7 is a view similar to Figures 4 and 5, showing the tools in position after the accomplishment of the first step of the' modified process.

Figure 8-15 a perspectiveview of a rivet incorporated in a'seam in accordance with the present invention, produced by either the preferred or by the modifiedlprocess. The primary objective in a riveted joint is adequate strength and resistance to' separation of the sheets, whether under the influence of a out their entire. perimeters, with the sheets,.and

by-like intimate and uniform association of the rivet shank with the edges ofqthe holes. By

principles whereof will be more particularly desuch intimate and uniform association of'heads and shank a further obiectiveis attained, namely, the avoidance of the possibility of leakage beneath the heads and along the shank through the holes. Imperfections in riveting result largely from laterally offset or misplaced upset heads, or from cocking of the rivet shank in the holes. Such shanks, being necessarily initially smaller than the holes, so that they may be inserted readily, may in the process of upsetting the head on the shank become cocked so that their axis does not coincide with the common axis of the holes, and in addition to causing offsetting of the upset heads such cocking may raise the preformed head at one side from the sheet, so that such head does not bear upon the sheet about its entire perimeter, and the cooked shank may not expandto contact the edges of the holes adequately about its entire periphery. Too large a percentage of imperiect rivets may result in failure of the Joint, or leakage. If, in order to. compensate for the expected imperfections oi the rivets an excess number is used, the riveting operations become unduly expensive and time-consuming, and add in the aggregate to the weight of the airplanean important consideration. By the process to be described a high percentage of perfect rivets may be expected, with the consequent obvious advantages. In addition there is achieved the end, particularly desirable in aircraft work, of forming, when desired, a flush headed rivet, though using to start a rivet with a rounded or upwardly bulged head.

The process will be described in connection with the joining of what, for convenience, may be designated the uppersheet A and the lower sheet B, and while two such sheets are shown here. the process is equally adapted to the joining of three or more sheets, within reason, one of which may be, for instance, the flange of a structural member. These sheets are drilled or punched to provide registering holes through which the shank 2 of a suitable rivet-is passed, the rivet having a rounded or upwardly bulged head I, as shown in Figure 1. The under side of the head I preferably forms a right-angledshoulder upon theshank 2. The shank 2 is slightly less in diameter than the holes through the sheets A and B, as is normal with all rivets, so that it may be passed through the holes without undue resistance. In the drawing this clearance has been shown somewhat exaggeratedly, but due to this clearance, if it be attempted to upset the shank to form a head, the rivet very frequently cocks in the holes, and the upset head is offset or otherwise irregular and imperfect, hence unsatisfactory. To avoid this, and for other reasons, it is desirable to expand that portion of theshank which is within the holes radially into intimate association with the edges of the holes. The length of the shank is carefully chosen to this end, in accordance with the thickness of the sheets, and other considerations hereafter discussed.

If we consider the insertion oi the rivet as the first step, as shown in Figure l, the second step may be considered as comprising chiefly a reversal of the bulge of the head, although an equally important result, the radial expansion of the shank, is simultaneously accomplished. Whereas in Figme 1 the head I is bulged upwardly, at the completion of the second step the head is bulged downwardly, as seen in Figure 2, and to accom- ,modate the reversed bulge of the head the plates are counter-punched, preferably simultaneously with or during the second step. Thus in Figure 4 the rivet is shown inserted in place, andtwo tools, an anvil or bucking tool 3 and a hammer 4, are shown in position to commence the second step, the reversal of the bulge of the head I.

It will be noticed that the hammer 4 is sub-. stantially flat in that portion which engages the head I, and that it extends beyond the circle or perimeter of the head at all points, but needs no centering or positioning means. It is suflicient if the hammer 4 is large enough that, being approximately centered, it extends outside of the circle oithe head I, eventually to engage the upper sheet A outside this circle. The. anvil 3 likewise extends outside the circle of the head, to engage the underneath sheet B outside of this circle, and it has a depression 5 which is of such size and shape, or volumetric capacity, as to receive in effect the metal of the head I as the bulge of the latter is reversed by the hammer 4, or other flat means of applying force to the head. The anvil likewise has a hole 6 which receives the protruding shank 2, and thereby centers the anvil relative to the rivet and the holes in the sheets, and serves to deter or prevent cocking of the shank.

The centering hole Ii in the anvil is preferably,

'but not necessarily, slightly tapered, its bottom being smaller than its entrance. This tapering serves to center the anvil, but achieves a further result in that it permits some slight radial expansion of the shank between its end and the shoulder formed by its preformed head I, provided the shanks axial advance, due to reversal of the bulge of the head, is sufllciently resisted as to require the shank to expand thus. The depth of the hole 6 is so chosen, relative to the length of the protruding portion of the rivet shank, and relative to the expected axial advance of the shank which results from reversal of the bulge of the head I, that the end of the shank abuts the bottom of the hole 5 before the reversal of the bulge of the head is completed. The diameter of the bottom of the hole 8 being approximately equal to the diameter of the end of the rivet shank 2, and the two abutting prior to completion of the reversal of the bulge of the head, the shank must expand, and since its expansion within the taper of the hole 6 is quite limited, by proper choice of the volume of the hole, the shank expands in that portion which is within the holes in the sheets, and thereby is brought into intimate contact, about its entire periphery, with the edges of these holes. It is not headed, however, for the largest diameter of the hole 8, at its entrance, is only equal, or substantially equal, to the diameter of the holes in the sheets.

During the operation of reversing the bulge of the head I, thev downward force of the tool 4 is transmitted to the upper sheet A all around the circle of the perimeter of the head I, and'this force, reacting from the anvil 3 which initially and always contacts the lower sheet B at some distance outwardly from and all around the holes in the sheet, grips the plates A and B, between the perimeter oi the head 'I and the flat portion of the anvil, outside of the cup-like depression 5, but leaves the sheets free to be deformed inside this circle. The centering, as noted above, is accomplished, not by any engagement of the hammer with the rivet head, but by the reception of the shank 2 within the hole 6. The action of the force applied by the tool 4 is to flatten the head, thereby and simultaneously to depress or counterpunch the sheets A and B until they are cupped to the shape of the depression 5, and to expand the shank radially. As pointed out sequently to the counter-punching and shankabove, the size and shape of this depression is usually just calculated properly to effect the desired amount of counterpunching of the sheets A and B, and to leave a counterpunch depression in the upper sheet A of just suflicient volume to receive the now reversely bulged head, and to leave the head flush. The depth of the .hole 6 is just calculated to be suificient to be contacted by the end of the shank and to effect some resistance' to its endwlse movement, thereby giving it 0 a tendency to bulge outwardly or expand all around, and in all parts of its length. The result is shown in Figure 2, where the head, nowdesignated I0, is reversely bulged and flattened on its top flush with the surface of the sheet A. The shank is slightly bulged in its intermediate portion, into intimate contact all around the edges of the holes. The sheet A is counterpunched, as indicated at a, and the sheet B is similarly counterpunched as shown at b. The radius of curvature of the depression is fairly long, corresponding generally, though reverse in direction, to the radius of the original head I. The radius joining the edges of the depression to the surface of the sheet is preferably slight.

. compressed and held tightly between the com- As seen in Figure 2, the counterpunching of the sheets causes the inner edges of the holes, which before may have been precisely in registry, to depart slightly from registry, and there are formed thereby minute shoulders into and over which the shank bulges or expands, thereby securing the most intimate contact and association possible between the shank and the edges of the holes,,and by reason of these shoulders and the tapering of the edges of the holes, caused by the counterpunching, the expanded portion of the shank of the rivet is seated sufficiently tightly in the holes that it cannot readily be dislodged, nor cocked sidewise during a subsequent operation.

It is in effect tack-riveted, and if only light rivet- 40 ing is needed, the operation need not be carried further. I

It will be noted that the operation can he carried out in such a way that the rivet head is not brought flush with the surface of the upper sheet A, for this result depends upon the proper proportioning of the size and volume of the original head I, and of the depression 5. If the head I is originally of larger volume than the depression 5, then (disregarding compression of 5 the metal) a portion of the head will still be left upstanding above the upper surface of the upper sheet A. It will also be observed that the orig-' inal shape of the upwardly bulged head I need not be precisely as shown. It may indeed be, somewhat thicker toward its perimeter than the form shown, and in the riveting operation the metal of the head may be caused to flow in various ways and directions to accomplish the end or ends in view. no

It will also be noted that the hole 6 need not be tapered. Even tough not tapered, it will center the anvil relative to the rivet shank and to the holes in the sheets. Being tapered, it enables the rivet shank to be more easily fitted within it, yet may accomplish some slight lateral shifting of the anvil at the outset of the head-reversing operation, if the anvil and rivet are not then precisely coaxial.

The final step of the operation, assuming that more than tack-riveting is desired, is to upset the projecting portion of the rivet shank, that portion which has been tapered as indicated at 20, and this part of the operation is performed as a separate and distinct step, and always subexpanding operation. It is performed as shown in Figure 5 by applying force to the head III, as by striking the latter with the flat head of the hammer 4, and by employing a flat anvil or bucking tool 8 (which may be another face of the same tool that carries the depressions 5 and 6) to'upset the shank 20, and to form on the under .slde of the seam the upset head 2|, as seen in Figure 3. This final operation needs no centering, for it is only the normal operation of upsetting a head on a protruding shank. The rivet has already been fixed against cocking, hence a high percentage of substantially perfect heads 2| are readily formed by a normally skilled riveter. The upsetting of the head 2| is thus accomplished without any disturbance of the now flattened and reversely bulged head III, or of the relationship of the latter to the sheets A and B or to the counterpunches a and b. The head 2|, being unconfined round about, upsets and expands radially, and overlies the edges of the holes through the sheets, and the metal of the upset head 2| is materially compressed and the sheets entirely around the holes are pressed head l0 and the compressed upset head 2|. As pointed out above, the shank has previously been expanded radially into intimate association with the edges of the holes, and the result is that the rivet fits tightly at all points within and about the holes, holds tightly, and there is little likelihood of leakage or failure to hold.

In some locations, where clearances are slight,

the bucking tool 3 can only be removed by sidewise sliding, but when the shank 20 is within the recess 6 this is not possible; if the space is so restricted that the tool 3 cannot be lifted back off the shank, the process above cannot be followed exactly. Instead, the sheets may be counterpunched as shown in Figure 7, prior to the reversal of the bulge of the head. The counterpunching may be accomplished by suitably formed punch 1 and die 9, which, after the operation of counterpunching, are separately removed,

the inside one 9 by sidewlse sliding, leaving the sheets counterpunched as seen in Figure 6. In this view the rivet has now been inserted, as a second step, in the counterpunched holes. Following the step shown in Figure 6, a flat bucking tool is applied to the end of the shank, as before,

and the hammer is applied to the head I, and the latter ispressed inwardlyand its bulge reversed to fill up the depression defined by the counterpunches. Not so large a percentage of perfect heads can be produced thus, as by the preferred method first explained, for the reason that the shank is not expanded within the holes before the upsetting operation, yet the percentage is surprisingly high, and the modified method is used only in locations where, for reasons given, the preferred method can not be followed. It will be noted that, while the head-reversing and shank-upsetting operations are now simultaneous, the shank-upsetting operation still follows the previously performed counterpunching operation.

- The final result, according to either modification, is as shown in Figure 8. The head I0 is within a counterpuncheddepresslon in the sheet A, the sheet B is correspondingly counterpunched, and the entire exterior or upper surface is flush and smooth, provided, of course, the size of the head and of the counterpuncn forming devices have been properly calculated to that end. The

slight radius joining the edge of the depression with the flat surface of the sheet can be observed as a highlight, but is negligible. The sharper this radius, the less it is observable, yet to all intents and purposes the rivet head and sheet are precisely flush.

It has been proposed heretofore to accomplish simultaneously, as one operation, the counterpunching of the sheets, the reversal of the preformed head, and the upsetting of a head on the shank, and this I do not claim. Suchan operation has been found unsatisfactory. The reason may be that the rivet shank has no opportunity, prior to the upsetting, to expand radially into intimateassociation with the holes in the sheet, particularly as the edges thereof are simultaneously moving to a new location by the counterpunching, and do'not'beconie fixed in location until the end of the operation, so that the rivet shank has little or nothing which is fixed in position during the operation to prevent their cocking sidewise. In any event, such a method, wherein the three operations are performed in a single step, produces too high a percentage of offset upset heads, or otherwise imperfect rivets. By the present method, wherein the upsetting of the head 2| on the shank is performed as the final operation, subsequent to the counterpunching at least, wherever possible prior to the shank-expanding operation, and preferably I prior also to the head-reversing operation, the results have proven to be greatly superior. 1

It has also been proposed to effect a counterpunching operation by applying a hard washer,

suitably cupped, to the protruding shank of the rivet, eventually to be held in place by the upset head. Among other disadvantages, this has the disadvantages of extra expense and of added weight. By the present method the final rivet has no more weight than any corresponding adequate rivet, and requires no special preforming operation on the rivet.

What I claim as my invention is:

1. A method of riveting which comprises inserting a rivet having an upwardly bulged head within registering holes in a plurality of sheets to be joined, applying force to such head to flatten it and to reverse the bulge of the head, meanwhile backing the sheets in the vicinity of the circle of the head, to leave the reversed and flattened head substantially flush with the adjacently surrounding sheet, and, during such head-reversing operation engaging the protruding shank to effect its bulging, within the holes, but to'avoid itsmushrooming beyond the holes, and, asa separate and subsequent operation, upsetting a head upon the rivet shank.

2. A method of riveting which comprises inserting a rivet having a head within registering holes in a plurality of sheets to be joined, applyoutwardly about the holes, applying pressure, exerted over planes parallel to the general plane ing force to such head and to the protruding end of the shank to effect approach thereof and deformation of the intervening portion of the rivet, meanwhile backing the sheets in the vicining force to such head and to the protruding end of the shank to effect approach thereofand deformation of the intervening portion of the rivet, meanwhile backing the sheets in the vicinity of the circle of the head, to leave the head flat and substantially fiush with the adiacently surrounding sheet, and, during the described operation, confining the protruding shank to prevent its mushrooming, and, as a separate and subsequent operation, upsetting a head upon the protruding shank.

4. A method of riveting which comprises inserting a rivet within registering holes in a plurality of sheets to be joined with an end of the shank protruding at one side of the sheets, backing. the sheets at this side in a circle spaced of the sheets, to the rivet at its opposite ends, while confining the protruding end of the shank to prevent its material deformation, by such pressure effecting approach of the rivets ends, and leaving a head, at the side opposite the protruding shank, within a countersunk depression inside the aforesaid circle, and substantially flush with the sheet, and a shank expanded within the sure effecting approach of the rivets ends, and

leaving a head, at the side opposite the protruding shank, within a countersunk depression inside the aforesaid circle, and substantially flush with the sheet, a shank expanded within the holes, but not materially deformed in its protruding portion, and, as a separate and subsequent operation, upsetting a head upon the protruding rivet shank.

' LOUIS S; MARSH. 

